One of the most significant design innovations made possible by the introduction of plastic materials was the concept of the integral hinge, sometime referred to as the living hinge or film hinge. The integral hinge has been molded into a wide variety of products ranging from small bottle caps and jewelry boxes to large complex closures and housings. Hinges with one part biased toward either of two positions are also well known in the art. However, all of these biased hinges require a spring to achieve the snap or biasing action in addition to the two hinge members themselves.
The oil can principle is common in mechanic's oil cans wherein the oil can bottom is domed or bowed outward at its center. To dispense oil, the mechanic presses the bow with his thumb forcing it through a flat configuration to a reverse bowed position and thus reducing the volume of the oil can forcing the oil out. When the thumb pressure is released, the pressure is released, the internal forces stored in the distorted can bottom spring it back to its arched position.
Examples of snap action hinges typical of this prior art include U.S. Pat. No. 4,414,705, which includes the typically required third spring member in order to introduce the snap or biasing action into the hinge, and U.S. Pat. No. 3,289,877.
Other such hinges are shown in U.S. Pat. No. 3,545,034, which again shows a two part hinge, in this case connected by a hinge pin in the form of a bowed spring wire; in U.S. Pat. No. 3,760,972, which shows a container cover which is operable in response to pressure thereon; and in U.S. Pat. No. 4,095,712, which shows a container lid with a closable flap, and in which the lid is elastically deformable and is opened and closed in response to pressure on the minor part of the lid.